As the famous movie quote says, the job of a trial lawyer is to always be closing. From opening arguments through witness testimony, everything builds to closing arguments. Everything a trial lawyer has done throughout the trial is designed to peak during that final speech to the jury.
Of course, not all trials get to closing arguments. By this point, both sides have seen the strengths and weaknesses of the other case and had theirs tested as well. Should one side feel their case is not strong enough, offers may start to go back and forth and a settlement struck. If both sides are confident in the merits of their respective cases, then the trial lawyers proceed to closing.